【Daily Question 20090328】Popularizing knowledge of instruments (already summarized)

1. What are the basic units of the International System of Units? (The international units in both Chinese and English are required.) Length: meter (m); Mass: kilogram (kg); Time: second (s); Current: ampere (A); Thermodynamic temperature: Kelvin (K); Amount of substance: mole (mol); Luminous intensity: candela (cd). 2. Briefly describe the 3 basic ways of heat transfer? There are three basic modes of heat transfer: thermal conduction, convective heat transfer, and radiative heat transfer. 3. Describe the temperature measurement principle of thermoresistors. Principle: The resistance value of a metal conductor increases as the temperature rises. 4. Briefly describe the intermediate conductor law of thermocouples. Law of the intermediate conductor: When an intermediate conductor (a third conductor) is inserted into a thermocouple circuit, as long as the temperatures at both ends of the intermediate conductor are the same, its inclusion has no effect on the total potential of the thermocouple circuit. 5. Briefly describe the temperature measurement principle of thermocouples. The principle is: the thermoelectric effect. The thermoelectric effect is the phenomenon in which conductors or semiconductors A and B, made of two different materials, form a circuit; when there is a temperature difference between their two junctions, an electromotive force is generated between them, resulting in the flow of current within the circuit.

1. What are the basic units of the International System of Units? (Write the international units in both Chinese and English.) Length: meter, m; Mass: kilogram, kg; Time: second, s; Current intensity: ampere, A; Thermodynamic temperature: Kelvin, K; Amount of substance: mole, mol; Luminous intensity: candela, cd. 2. Briefly describe the 3 basic ways of heat transfer? Heat conduction, convection, and radiation. 3. Describe the temperature measurement principle of thermal resistors. Temperature measurement is carried out by utilizing the property that the resistance of conductors or semiconductors changes with temperature. 4. Briefly describe the intermediate conductor law for thermocouples. In a closed circuit composed of several different conductive materials, as long as the temperatures at the points where they are connected to each other are the same, the algebraic sum of the thermoelectromotive forces generated at each point in the circuit is zero. 5. Briefly describe the temperature measurement principle of thermocouples. It is based on the Seebeck effect: when two conductors of different materials are connected at both ends to form a circuit, and if the temperatures at these two connections differ, an electromotive force is generated within the circuit. This phenomenon is known as the thermoelectric effect, and such an electromotive force is called a thermoelectromotive force.

1. Basic units of SI:
Name of physical quantity, Name of unit, Unit symbol
Length, Meter, m
Mass, Kilogram, kg
Time, Second, s
Electric current, Ampere, A
Thermodynamic temperature, Kelvin, K
Luminous intensity, Candela, cd
Amount of substance, Mole, mol

2. Heat conduction, Convection, Thermal radiation

3. Thermal resistance is a method of temperature measurement based on the thermal effect of resistance; that is, the characteristic by which the resistance value of a resistive element changes with temperature. 4. By introducing a third conductor into the thermocouple circuit, as long as the temperatures at both ends of the conductor are the same, the inclusion of this conductor has no effect on the total potential of the thermocouple circuit. 5. The basic principle of thermocouple temperature measurement is to weld together two conductors or semiconductors made of different materials to form a closed circuit. Since the two different metals have different numbers of electrons, when there is a temperature difference between two points in two conductors, charge flows from the higher potential to the lower potential, thereby generating an electric current in the circuit. The greater the temperature difference, the larger the current. This phenomenon is known as the thermoelectric effect, or the Seebeck effect. Thermocouples work by utilizing this effect.

Too late: The answer from Floor L was great; I learned something from it. There are also derived units: Pressure: Pa, Speed: meters per second —— m/s, Density: g/m3 ..........................................

The three basic modes of heat transfer are: radiation, convection, and conduction.

1. Length: meters (m； Mass: kilograms (kg ； Time: seconds (s) ； Current: Ampere (A) ； Thermodynamic temperature: Kelvin (K) ； Amount of substance: mole (mol) ； Luminous intensity: candela (cd). 2. There are three types of heat transfer: conduction, convection, and radiation. 3. Principle of temperature measurement: The resistance value of a resistive element changes as the temperature changes. 4. Law of the intermediate conductor: When using thermocouples for temperature measurement, it is necessary to introduce connecting wires and instruments into the circuit. Will the presence of these connecting wires and instruments affect the thermoelectric potential in the circuit? The intermediate conductor law states that in a thermocouple temperature measurement circuit, when a third conductor is introduced, as long as the temperatures at both ends of this third conductor are the same, it has no effect on the total thermoelectromotive force of the circuit. 5. Principle of temperature measurement using thermocouples: Two conductors (or semiconductors) made of different materials form a closed circuit. When the temperatures at the two junctions are T and T0 and these values are not equal, an electromotive force is generated within this circuit. This phenomenon is known as the thermoelectric effect, and the electromotive force generated is called the thermoelectromotive force. The combination of these two different materials, either conductors or semiconductors, is called a thermocouple, with conductors A and B being referred to as thermal electrodes. There are two contacts: one is called the hot terminal, also known as the measuring terminal or working terminal, and it is placed in the medium being measured during temperature detection; the other is called the cold terminal, also known as the reference terminal or free terminal, and it is connected to the display instrument through wires. Thermoelectric potential is a type of electromotive force that arises at the two ends of the same conductor due to differences in temperature. When the temperatures at the two ends of a conductor are different, the electrons at the higher-temperature end possess greater energy than those at the lower-temperature end. As a result, more electrons move from the higher-temperature end to the lower-temperature end than vice versa. The higher-temperature end thus becomes positively charged due to the loss of electrons, while the lower-temperature end becomes negatively charged due to the accumulation of excess electrons. This leads to the formation of a contact potential between the two ends of the conductor. For a given thermocouple, when the temperature of the reference terminal T0 remains constant, eAB(T0) = c is a constant; consequently, the total electromotive force is a function of temperature T only, that is, eAB(T – T0) = eAB(T) – c = f(T). This is the principle behind using thermocouples for temperature measurement.